The insulator running outdoors will be polluted by dust, soot and industrial discharge, and the pollution layer on the porcelain surface, the contaminated insulator can be flashover along the surface under the voltage action, and the flashover voltage is referred to as pollution lightning.

In dry condition, the flashover voltage of insulators is not affected by surface pollution, but in the fog, dew, snow, drizzle and other climatic conditions, insulator surface contamination layer damp, its flashover voltage greatly reduced, resulting in pollution flashover accident, even at work voltage will occur pollution flashover accident. Pollution flashover accident is characterized by long time, generally can not be used to eliminate automatic closing, the accident is easy to expand, resulting in large areas of power outages, repair and recovery time is long, seriously affecting the safe operation of power systems.